people and cattle. You should see the active Bee at work when the road
is dazzling white under the rays of a hot sun. Between the adjoining
farm, which is the building-yard, and the road, in which the mortar is
prepared, we hear the deep hum of the Bees perpetually crossing one
another as they go to and fro. The air seems traversed by incessant
trails of smoke, so straight and rapid is the worker's flight. Those
on the way to the nest carry tiny pellets of mortar, the size of small
shot; those who return at once settle on the driest and hardest spots.
Their whole body aquiver, they scrape with the tips of their mandibles
and rake with their front tarsi to extract atoms of earth and grains
of sand, which, rolled between their teeth, become impregnated with
saliva and form a solid mass. The work is pursued so vigorously that
the worker lets herself be crushed under the feet of the passers-by
rather than abandon her task.

On the other hand, the Mason-bee of the Walls, who seeks solitude, far
from human habitations, rarely shows herself on the beaten paths,
perhaps because these are too far from the places where she builds. So
long as she can find dry earth, rich in small gravel, near the pebble
chosen as the site of her nest, that is all she asks.

The Bee may either build an entirely new nest on a site as yet
unoccupied, or she may use the cells of an old nest, after repairing
them. Let us consider the former case first. After selecting her
pebble, the Mason-bee of the Walls arrives with a little ball of
mortar in her mandibles and lays it in a circular pad on the surface
of the stone. The fore-legs and above all the mandibles, which are the
mason's chief tools, work the material, which is kept plastic by the
salivary fluid as this is gradually disgorged. In order to consolidate
the clay, angular bits of gravel, the size of a lentil, are inserted